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Synchronous Serial Interface

8.2.9.12 Transmit Frame Sync (TFS)—Bit 3

When set, the transmit frame sync (TFS) flag bit indicates that a frame sync occurred during transmission of the last word written to the STX register. Data written to the STX register during the time slot when the TFS bit is set is sent during the second time slot (in network mode) or in the next first time slot (in normal mode). In network mode, the TFS bit is set during transmission of the first slot of the frame. It is then cleared when starting transmission of the next slot. The TFS bit is cleared by DSP, SSI, or STOP reset.

8.2.9.13 Receive Frame Sync (RFS)—Bit 2

When set, the receive frame sync (RFS) flag bit indicates that a frame sync occurred during reception of the next word into the SRX register. In network mode, the RFS bit is set while the first slot of the frame is being received. It is cleared when the next slot of the frame begins to be received. The RFS bit is cleared by DSP, SSI, or STOP reset.

NOTE:

In synchronous mode (the SCR2’s SYN bit is set to one), the RFS bit is not valid. In asynchronous mode (the SYN bit is cleared), the RFS bit indicates the state of the SRFS pin. (See section Section 8.3, “SSI Data and Control Pins,” for details on the SRFS pin.) When the SSI is being used in synchronous mode, the TFS bit should be used to check the state of the STFS pin, since that pin is used for both transmit and receive frame sync in synchronous mode.

8.2.9.14 Receive Data Buffer Full (RDBF)—Bit 1

The receive data buffer full (RDBF) flag bit is set when the receive section is programmed with the receive buffer enabled, and the contents of the RXSR are transferred to the receive data buffer register. When set, RDBF indicates that data can be read from the SRX register. Note that an interrupt is only generated if both the RDF and RIE bits are set. The RDBF bit is cleared by DSP, SSI, or STOP reset.

8.2.9.15 Transmit Data Buffer Empty (TDBE)—Bit 0

The transmit data buffer empty (TDBE) flag bit is set when the transmit section is programmed with the transmit buffer enabled and the contents of the transmit data buffer register are transferred to the TXSR. When set, the TDBE bit indicates that data can be written to the STX register. Note that an interrupt is generated only if both the TDE and the TIE bits are set. The TDBE bit is set by DSP, SSI, or STOP reset.

8.2.10 SSI Time Slot Register (STSR)

The SSI time slot register (STSR) is used when data is not to be transmitted in an available transmit time slot. For the purposes of timing, the time slot register is a write-only register that behaves like an alternate transmit data register, except that instead of transmitting data, the STD pin is tri-stated. Using this register is important for avoiding overflow or underflow during inactive time slots.

8-18

DSP56824 User’s Manual

 

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